recover deleted previews

Thanks for all the thoughts but I'm still in the dark. For the record I back up all my images onto multiple drives. That's not the issue. I've refined my description of the problem and include it below with the hope one of you more adept souls can see through the haze that alficts me on this problem.

I use Smugmug as my web portfolio platform. Using the Smugmug plugin in Lightroom I intended to sync my portfolio galleries on my Smugmug site with the associated folders in my Publish Services feature in Lightroom. 

I THINK what I did was instead of just syncing “Folders and Galleries” I failed to unclick the “sync photos” check box. I went away from the computer for dinner. Returning hours later I discovered that Lightroom was still syncing, when it should have been done with the small job in a matter of minutes. Lightroom, which in my case contains 330,000 images, was attempting to link all those images with Smugmug, where I have only a couple of thousand images (a couple of hundred in my portfolio and most in client web galleries). It seems that the process any thumbnails from Lightroom that did not have a counterpart in Smugmug were removed .

I’m using bare drives in docks. When I open Lightroom I can see the previews ONLY for the image files on the specific drives that are installed and running.  I can’t see the previews (ie preview.lrdata) for  image files that are on drives not installed and running. So where are they and how can I see them when the drive is not installed and running ?  With so many images and drives I really need to be able to see the previews all the time so I can find older images when needed without constantly stuffing hard drives in and out of the docks. This all used to work just fine... argh.

When I tried the command to make new standard previews,  (hoping that would somehow resurrect my previews.lrdata) as Ian suggested above LR tells me that they already exist and are up to date. This makes me assume the previws still exist. Why they won't show up as they used to regardless of whether or not the source drive is installed and running is a mystery to me. My question is how do I get them back? Should I bring in a backup version of the previews.lrdata to resolve this issue? If so what is the process.

When I go to open the backup Lightroom wants to update to the latest version and won’t let me do anything unless I comply!! I don’t want to do that for fear such and updat will just complicate matters.

Does all this make sense to any of you, my respected colleagues?

Many thanks,

Dan